a(n) = 5^C(n,2)*(5^n-1)/4.A127849a(n) = 5^C(n,2)*(5^n-1)/4.Terms a(0) =0a(1) =1a(2) =30a(3) =3875a(4) =2437500a(5) =7626953125External referencesoeis: A127849